Plasmon-Enhanced Raman Scattering by Carbon Nanotubes Optically Coupled with Near-Field Cavities

We realize the coupling of carbon nanotubes as a one-dimensional model system to near-field cavities for plasmon-enhanced Raman scattering. Directed dielectrophoretic assembly places single-walled carbon nanotubes precisely into the gap of gold nanodimers. The plasmonic cavities enhance the Raman signal of a small nanotube bundle by a factor of 10(3). The enhanced signal arises exclusively from tube segments within the cavity as we confirm by spatially resolved Raman measurements. Through the energy and polarization of the excitation we address the extrinsic plasmonic and the intrinsic nanotube optical response independently. For all incident light polarizations, the nanotube Raman features arise from fully symmetric vibrations only. We find strong evidence that the signal enhancement depends on the orientation of the carbon nanotube relative to the cavity axis.